In WLANs, a CCAT is specified to define a threshold for received signal strength above which a WLAN node, e.g. an Access Point, AP, or a wireless device, STA, will sense the transmission of other WLAN devices to avoid transmission collision.
Generally, one CCAT may be defined for all the nodes in the system regardless of the location and radio condition of each individual node; or every node may determine the CCAT independently of other nodes. A default value, e.g. −82 dBm, may be defined that the nodes may use. This may not be optimal in all different situations since the CCAT may be optimised based on the local condition of each wireless device in order to improve both user experience and system efficiency.
When a node wishes to perform a transmission, the node senses the channel, this is often referred to as listens to the channel. The procedure is sometimes referred to as Listen-Before-Talk. The node may receive signals and/or transmissions from other nodes in the LAN, wherein the node receives a certain received power. The node may then compare the received power to the CCAT, and if the received power is above the CCAT, the node concludes that the channel is busy and refrains, or backs off, from transmitting on the channel. If the received power is below the CCAT, the node concludes that the channel is free and may initiate a transmission to another node.
A threshold for the wireless devices based on received power from their AP has been proposed to be used in order for the wireless devices to determine whether a channel is free or busy. However, this may not be optimal from a performance perspective, since it does not include any information about the interference situation of the wireless device. In other words, nodes in the network may be prevented from transmitting even though the transmission is likely to be successful and not disturb other ongoing transmissions.
Yet another solution has been proposed, e.g. in EP2775776, where the CCAT is determined based on previous receptions of packets.